1. Field of the Invention
The present invention relates to oscillators, methods for producing oscillators, and communication apparatuses incorporating oscillators.
2. Description of the Related Art
Conventionally, an oscillator used for a high frequency circuit, such as a microwave band frequency circuit, includes a resonance circuit, which is defined by transmission lines such as a microstrip line and chip components such as capacitance elements disposed on a circuit substrate, and an amplifier amplifying a resonance signal output from the resonance circuit.
In each conventional oscillator formed by packaging oscillation circuits composed of components mounted on printed circuit substrates, first, electrode patterns are provided in oscillation-circuit forming sections on a printed circuit assembly board used to produce a plurality of oscillators. Then, chip components are mounted on the electrode patterns, and connections are made by reflow soldering. After that, the printed circuit assembly board is divided into oscillation-circuit forming sections to adjust the oscillation frequency of the various sections. Finally, a metal cover is attached to the assembly board to complete the product.
In the conventional oscillators including the resonance circuits defined by the transmission lines such as microstrip lines provided on the printed circuit assembly board, however, variations in impedance between the transmission lines occur, particularly, variations in inductance between the transmission lines. In addition, there are variations in impedance between the chip components, such as chip capacitors defining the resonance circuits together with the transmission lines. Thus, the oscillation frequencies of the oscillators are higher or lower than a design value. As a result, trimming each of the transmission lines disposed on the circuit assembly board is required to make adjustments to obtain a desired oscillation frequency. Such a process causes the following problems.
Since frequency adjustment time is necessary, production time is greatly increased, thereby substantially increasing cost. In addition, laser trimming requires an expensive laser trimming apparatus. Furthermore, since the time-consuming laser trimming carbonizes the transmission lines, this results in a lower Q of the resonators, thereby deteriorating the characteristics of oscillators, such as C/N ratio characteristics.
Furthermore, since electrode lands for trimming are necessary, the entire oscillator cannot be miniaturized.
To overcome the above-described problems with the prior art, preferred embodiments of the present invention provide an oscillator which greatly reduces production time and cost and which achieves miniaturization without deteriorating the electrical characteristics. In addition, preferred embodiments of the present invention provide a method for producing the oscillator and a communication apparatus incorporating the oscillator.
According to a first preferred embodiment of the present invention, a method for producing an oscillator includes a resonance circuit including a transmission line provided on a circuit substrate and chip components mounted on the circuit substrate and an amplifying circuit amplifying a resonance signal of the resonance circuit. The oscillator producing method includes the steps of measuring the impedance of the transmission line of the resonance circuit when the transmission line is disposed on the circuit substrate, determining the impedances of chip components included in the resonance circuit, selecting chip components having impedances required to obtain a desired oscillation frequency from the chip components according to the transmission line impedance to mount on the circuit substrate, and mounting the chip components on the circuit substrate.
As described above, according to the impedance of the transmission line provided on the circuit substrate, chip components having impedances required to obtain the desired oscillation frequency are selected and mounted on the circuit substrate. With this arrangement, without trimming the transmission line, an oscillator oscillating at the predetermined oscillation frequency is obtained. As a result, since frequency-adjustment time is not required and it is unnecessary to use a trimming apparatus, no deterioration in the electric characteristics due to laser trimming occurs. In addition, since it is unnecessary to provide an electrode land for making frequency adjustments, the entire oscillator is miniaturized.
Furthermore, in the oscillator-producing method described above, the circuit substrate may be a circuit assembly board, on which a plurality of oscillator-forming sections is provided, and in this state, measuring the impedance of each transmission line and mounting the chip components are performed. In this manner, on the circuit assembly board, chip components such as chip capacitors are individually selected and mounted according to the impedances of the transmission lines disposed in the sections where the oscillation circuits are provided. Thus, since it is unnecessary to measure the impedances of the transmission lines as individual components, the transmission line impedances are easily measured.
According to a second preferred embodiment of the present invention, an oscillator includes a resonance circuit including a transmission line provided on a circuit substrate and chip components mounted on the circuit substrate, an amplifying circuit connected to the resonance circuit to amplify a resonance signal output from the resonance circuit, and an electrode land provided on the circuit substrate and electrically connected to the transmission line and abutting the probe of a measurement apparatus for measuring the impedance of the transmission line. Using of the circuit substrate having the oscillator, the transmission line impedance is easily measured. Since the position of the electrode land is fixed on the circuit substrate, the measurement of the transmission line impedance can be automated.
According to a third preferred embodiment of the present invention, a communication apparatus incorporating the oscillator is provided having the above-described novel structure. For example, the communication apparatus is produced by using the oscillator as a local oscillation circuit. With this arrangement, a compact and low-priced communication apparatus is obtained.
Other features, characteristics, elements and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.